Sliding parts

ABSTRACT

By randomly arranging dimples provided on a sealing face, a sliding characteristic is improved in a wide range of a bearing characteristic number on the sealing face. A pair of sliding parts in which a plurality of dimples is arranged on at least one of sealing faces that relatively slide on each other is characterized in that each of the plurality of dimples is provided independently from the other dimples, and arranged in such a manner that the plurality of dimples having different opening diameters is randomly distributed.

TECHNICAL FIELD

The present invention relates to sliding parts suitable for a mechanicalseal, a bearing, and other sliding portions for example. In particular,the present invention relates to sliding parts such as a sealing ring ora bearing in which a fluid lies on sealing faces to reduce friction andthere is a need for preventing fluid leakage from the sealing faces.

BACKGROUND ART

In order to maintain a sealing property for a long time in a mechanicalseal serving as one example of sliding parts, contradictory conditionsof “sealing” and “lubricity” have to be met at the same time. In recentyears especially, there has been an even greater demand for lowerfriction in order to reduce mechanical loss while preventing leakage ofa sealed fluid for environmental measures or the like. Lower friction isto be realized by applying various texturing to a sealing face. Forexample, there is a known method of arranging dimples on a sealing faceas one of the texturing.

For example, in the invention described in JP 11-287329 A (hereinafter,referred to as “Patent Citation 1”), by forming a large number ofdimples having different depth on a sealing face, a load capacity due toa fluid bearing pressure generated in a fluid lying between the sealingface and the opposing sealing face at the time of sliding is decreasedat part of the dimples in accordance with a change in a fluidtemperature but increased at the other dimples. Thus, the load capacityis stabilized and an effect of always maintaining a preferable slidingproperty can be obtained irrespective of a temperature change.

In the invention described in JP 2000-169266 A (hereinafter, referred toas “Patent Citation 2”), by forming a sealing face by depositing a hardfilm on a surface of a base member made of a sintered ceramic materialand providing a large number of dimples on this sealing face, wearresistance is improved and a liquid lubricating property by the dimplesis improved.

CITATION LIST Patent Literature

Patent Citation 1: JP 11-287329 A

Patent Citation 2: JP 2000-169266 A

SUMMARY OF INVENTION Technical Problem

However, the invention described in Patent Citation 1 focuses on thedepth of the dimples provided on the sealing face for always maintaininga preferable sliding property irrespective of the temperature change butan influence of opening diameters of the dimples on a slidingcharacteristic (reduction in friction coefficient) has not yet beenexamined.

The invention described in Patent Citation 2 is to improve the liquidlubricating property by providing the dimples on the sealing face.However, as well as Patent Citation 1, an influence of opening diametersof the dimples on a sliding characteristic (reduction in frictioncoefficient) has not yet been examined.

An objective of the present invention is to provide sliding partscapable of improving a sliding characteristic in a wide range of abearing characteristic number on a sealing face by randomly arrangingdimples provided on the sealing face.

Solution to Problem

In order to achieve the foregoing objective, a first aspect of thepresent invention is a pair of sliding parts in which a plurality ofdimples is arranged on at least one of sealing faces that relativelyslide on each other characterized in that each of the plurality ofdimples is provided independently from the other dimples, and arrangedin such a manner that the plurality of dimples having differentdiameters is randomly distributed.

According to the first aspect, in the wide range of the bearingcharacteristic number on the sealing face, the sliding characteristiccan be improved, that is, the friction coefficient can be reduced.

A second aspect of the sliding parts of the present invention relates tothe first aspect, characterized in that the opening diameters of theplurality of dimples are set within a range from 30 to 100 μm.

According to the second aspect, in the wide range of the bearingcharacteristic number on the sealing face, the sliding characteristiccan be furthermore improved.

A third aspect of the sliding parts of the present invention relates tothe first or second aspect, characterized in that depth of the pluralityof dimples is set within a range from 50 to 1,000 nm.

According to the third aspect, the friction coefficient on the sealingface can be reduced.

A fourth aspect of the sliding parts of the present invention relates toany of the first to third aspects, characterized in that the depth ofthe plurality of dimples is set within a range from 100 to 200 nm.

According to the fourth aspect, the sliding characteristic at extremelylow speed on the sealing face can become preferable.

A fifth aspect of the sliding parts of the present invention relates toany of the first to fourth aspects, characterized in that an area ratioof the plurality of dimples relative to the sealing face is 30 to 50%.

According to the fifth aspect, sealing and lubricity on the sealing facecan be obtained at the same time.

Advantageous Effects of Invention

The present invention exhibits the following superior effects.

(1) Since each of the plurality of dimples is provided independentlyfrom the other dimples, and arranged in such a manner that the pluralityof dimples having different diameters is randomly distributed, thesliding characteristic can be improved in the wide range of the bearingcharacteristic number on the sealing face.

(2) Since the opening diameters of the plurality of dimples are setwithin a range from 30 to 100 μm, the sliding characteristic can befurthermore improved in the wide range of the bearing characteristicnumber on the sealing face.

(3) Since the depth of the plurality of dimples is set within a rangefrom 50 to 1,000 nm, the friction coefficient on the sealing face can bereduced.

(4) Since the depth of the plurality of dimples is set within a rangefrom 100 to 200 nm, the sliding characteristic at extremely low speed onthe sealing face can become preferable.

(5) Since the area ratio of the plurality of dimples relative to thesealing face is 30 to 50%, the sealing and the lubricity on the sealingface can be obtained at the same time.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is to illustrate one example of a sealing face of a sliding partaccording to an embodiment of the present invention: FIG. 1(a) is a planview of the sealing face; FIG. 1(b) is an A-A sectional view; and FIG.1(c) is a B-B sectional view;

FIG. 2 is a plan view of the sealing face showing dimples randomlyarranged on the sealing face of the sliding part according to theembodiment of the present invention;

FIG. 3 is a chart showing diameter size distribution of the randomlyarranged dimples according to the embodiment of the present invention;

FIG. 4 is a chart showing a relationship between a friction coefficientand a bearing characteristic number G obtained by a rotation slidingtest; and

FIG. 5 is a schematic sectional view for illustrating a testing machinecapable of measuring sliding torque, the testing machine used in thepresent test.

DESCRIPTION OF EMBODIMENTS

Hereinafter, with reference to the drawings, a mode for carrying out thepresent invention will be described and exemplified based on anembodiment. However, regarding size, material, shape, and relativearrangement of constituent parts described in the embodiment, and thelike, there is no intention to limit the scope of the present inventiononly to those unless specifically and clearly described.

EMBODIMENT

With reference to FIGS. 1 to 5, a sliding part according to theembodiment of the present invention will be described.

As shown in FIG. 1(a), a sliding part 1 is formed in an annular body. Ingeneral, a high pressure sealed fluid exists on one side of inner andouter peripheries of a sealing face S of the sliding part 1, and theatmosphere is on the other side.

This sealed fluid can be effectively sealed by using the sliding part 1.For example, this sliding part 1 is used for at least one of a pair ofrotating and stationary sealing rings in a mechanical seal device. Byclosely placing a sealing face of the rotating sealing ring and theopposing sealing face of the stationary sealing ring, a sealed fluidthat exists in one of inner and outer peripheries of the sealing facesis sealed.

The sliding part can also be utilized as a sliding part of a bearingthat slides on a rotating shaft while sealing lubricating oil on oneside in the axial direction of a cylindrical sealing face.

In the present example, a mechanical seal serving as one example of thesliding part will be described as an example. In the description, anouter peripheral side of the sliding part that forms the mechanical sealserves as a high pressure fluid side (sealed fluid side), and an innerperipheral side serves as a low pressure fluid side (atmosphere side).However, the present invention is not limited to this but can also beapplied to a case where the high pressure fluid side and the lowpressure fluid side are set the other way around. In FIG. 1, forconvenience of description, a case where the high pressure sealed fluidexists on the outer peripheral side will be described.

In the example shown in the figures, a sectional shape of the slidingpart 1 is a convex shape as shown in FIG. 1(c), and a top face thereofforms the flat sealing face S. A large number of dimples 2 as shown inFIG. 1(b) are independently provided on this sealing face S. Thesedimples 2 are provided not over the entire width in the radial directionof the sealing face S but in dimple formation regions 3 close to thehigh pressure fluid side. The dimple formation regions 3 communicatewith the high pressure fluid side and are isolated from the low pressurefluid side by a flat seal face 4.

In the present example, the case where the dimples 2 are provided in thedimple formation regions 3 arranged equally and independently in thecircumferential direction is shown. However, the present invention isnot limited to this but the dimples may be provided continuously in thecircumferential direction. In the present example, the sliding part 1 ismade of silicon carbide (SiC).

In the present invention, the “dimples” are dents formed on the flatsealing face S, and a shape thereof is not particularly limited. Forexample, a planar shape of the dents includes various shapes such as acircular shape, an oval shape, an oblong shape, or a polygonal shape,and a sectional shape of the dents also includes various shapes such asa bowl shape or a square shape.

A large number of dimples 2 formed on the sealing face S have a functionof holding part of a liquid placed between this sealing face S and theopposing sealing face that relatively slides on the above sealing faceas a hydrodynamic lubricating liquid film so as to stabilize alubricating liquid film.

FIG. 2 is a plan view of the sealing face showing the dimples randomlyarranged on the sealing face of the sliding part according to theembodiment of the present invention. In FIG. 2, the same reference signsas the reference signs in FIG. 1 denote the same members as those inFIG. 1 and detailed description thereof will be omitted.

In FIG. 2, each of the plurality of dimples 2 formed on the sealing faceis provided independently from the other dimples, and arranged in such amanner that the plurality of dimples having different opening diametersis randomly distributed. As a method of random distribution of theopening diameters of the dimples, in the present example, decision ismade by using random numbers and the dimples are uniformly distributedon the sealing face. That is, setting is made in such a manner that thedistribution of the dimples having different opening diameters isuniform over the entire sealing face.

One example of a method of processing the dimples on the sealing facewill be described as follows.

(1) Decide diameters and positions of holes formed on a metal mask byusing random numbers.

(2) Form holes on the metal mask by means of laser processing accordingto the decided diameters and positions.

(3) Install the metal mask in which the holes are randomly formed on thesealing face of the target sliding part.

(4) Form the dimples on the sealing face by utilizing the holes of themetal mask by irradiation with a femtosecond laser from the upper sideof the metal mask, ion etching, or the like. The dimples havingdifferent opening diameters are uniformly arranged on the sealing facein predetermined distribution.

FIG. 3 is a chart showing diameter size distribution of the randomlyarranged dimples 2 according to the embodiment of the present invention.

In the present example, the opening diameters of the plurality ofdimples 2 are distributed within a range from 30 to 100 μm. More dimples2 having smaller opening diameters are distributed in comparison to thedimples 2 having larger opening diameters.

Random distribution of the opening diameters of the plurality of dimples2 is set in accordance with a bearing characteristic number G (fluidviscosity×speed/load) of the sealing face or the like. FIG. 3 shows onefavorable example in the mixed dimples having the opening diameters of30 to 100 μm.

Specifications of sliding parts used in the embodiment and a comparativeexample are shown in Table 1 below.

In the embodiment, the mixed dimples in which the opening diameters ofthe dimples 2 are randomly distributed within a range from 30 to 100 μmare used.

In the comparative example, single dimples in which the openingdiameters of the dimples 2 of three types including 50 μm, 75 μm, and100 μm are uniformly distributed on the sealing face are used.

Further, 100 nm is adopted as depth of the plurality of dimples 2 inboth the embodiment and the comparative example since a slidingcharacteristic at extremely low speed is preferable.

It should be noted that the depth of the plurality of dimples 2 ispreferably set within a range from 50 to 100 nm from a viewpoint ofreduction in a friction coefficient. However, in a case where importanceis attached to the sliding characteristic at extremely low speed, thedepth is preferably set within a range from 100 to 200 nm.

In order to obtain both sealing and lubricity at the same time, 40% isadopted as an area ratio of the plurality of dimples relative to thesealing face. However, the present invention is not limited to this butthe area ratio may be 30 to 50%.

TABLE 1 Example Comparative Example Inner diameter of φ 18 mm φ 18 mmsealing face Width of sealing 1.8 mm 1.8 mm face Dimple area ratio 40%40% Dimple opening φ 30 to 100 μm φ 50 μm, φ 75 μm, φ diameter mixed 100μm Dimple depth 100 nm 100 nm

Test conditions of the embodiment and the comparative example are shownin Table 2 below.

TABLE 2 SiC (dimple processing) × SiC Sliding material combination (noprocessing) Attachment load 25N Peripheral speed 0.0 m/sec → 10.0 m/secPressure 0.15 MPaG (outer peripheral side) Temperature 60° C. Sealedfluid JIS K2234LLC 50% water solution

FIG. 4 is a chart showing a relationship between the frictioncoefficient and the bearing characteristic number G obtained by arotation sliding test.

In FIG. 4, in a rotation number range in the test, in the comparativeexample in which the opening diameters of the dimples are φ50 μm, φ75μm, φ100 μm, it is found that within a range where a value of thebearing characteristic number G exceeds 7.6×10⁻⁸, the greater theopening diameters of the dimples are, the more the friction coefficientis lowered. A fluid lubricity transition point (hereinafter, referred toas the “Gc point”) exists for each of the opening diameters of thedimples. In the comparative example of φ50 μm, φ75 μm, φ100 μm, it isfound that the smaller the opening diameters of the dimples are, themore the Gc point is shifted to the lower G side and further the morethe friction coefficient at the Gc point is lowered.

In the embodiment in which the opening diameters of the dimples aremixed from φ30 to 100 μm, within a range where the G value exceeds about6.0×10⁻⁸, the friction coefficient is almost the same as that of thediameter of φ100 μm, and within a range of 6.0×10⁻⁸ or less, the Gcpoint is shifted to the lower G side and further the frictioncoefficient at the Gc point is lowered. It is found that there is aneffect on the reduction in the friction coefficient in a wide rotationnumber range.

It should be noted that during the test, no leakage from the sealingface is generated in the present test.

Next, with reference to FIG. 5, a testing machine 10 capable ofmeasuring sliding torque, the testing machine used in the present testwill be described.

A main body part of the testing machine 10 includes a casing 13 thatsupports a stationary ring 11 in a non-rotation state via a spring 12, arotating shaft 14 rotatably inserted in an inner periphery of thiscasing 13, and a rotating ring 15 supported on an outer periphery ofthis rotating shaft 14, the rotating ring facing the stationary ring 11in the axial direction. A sealing target liquid L is enclosed into asealed space surrounded by the rotating ring 15, the casing 13, and therotating shaft 14.

As a characteristic of the present testing machine 10, hydrostatic gasbearings are adopted as bearing parts 16 on both sides, so that thesliding torque of the mechanical seal can be measured with highprecision. The torque is measured by two kinds of methods including atorque meter 17 and a cantilever type load cell 18, so as to eliminatemeasuring errors by double-checking.

Operations and effects of the sliding part according to the embodimentof the present invention are as follows.

(1) In the rotation number range in the test, the comparative example inwhich the opening diameters of the dimples are φ50 μm, φ75 μm, φ100 μmhas a tendency that within a range where the value of the bearingcharacteristic number G exceeds 7.6×10⁻⁸, the greater the openingdiameters of the dimples are, the more the friction coefficient islowered, and the smaller the opening diameters of the dimples are, themore the fluid lubricity transition point (hereinafter, referred to asthe “Gc point”) is shifted to the lower G side and further the more thefriction coefficient at the Gc point is lowered. Meanwhile, in theembodiment in which the opening diameters of the dimples are mixed fromφ30 to 100 μm, within a range where the G value exceeds about 6.0×10⁻⁸,the friction coefficient is almost the same as that of the diameter ofφ100 μm, and within a range of 6.0×10⁻⁸ or less, the Gc point is shiftedto the lower G side and further the friction coefficient at the Gc pointis lowered. There is an effect on the reduction in the frictioncoefficient in a wide rotation number range.

(2) The depth of the plurality of dimples 2 is preferably set within arange from 50 to 1,000 nm from a viewpoint of the reduction in thefriction coefficient. However, by setting the depth within a range from100 to 200 nm, the sliding characteristic at extremely low speed canbecome preferable.

(3) By setting the area ratio of the plurality of dimples relative tothe sealing face within a range from 30 to 50%, the sealing and thelubricity can be obtained at the same time.

The mode of the present invention is described with the aboveembodiment. However, specific configurations are not limited to thesemodes of the embodiment but modifications and additions within a rangenot departing from the gist of the present invention are also includedin the present invention.

For example, the example that the sliding part is used for at least oneof the pair of rotating and stationary sealing rings in the mechanicalseal device is described in the above embodiment. However, the slidingpart can also be utilized as a sliding part of a bearing that slides ona rotating shaft while sealing lubricating oil on one side in the axialdirection of a cylindrical sealing face.

For example, the case where the high pressure sealed fluid exists on theouter peripheral side is described in the above embodiment. However, thepresent invention can also be applied to a case where the high pressurefluid exists on the inner peripheral side. In that case, the dimples arearranged to communicate with the inner peripheral side.

For example, the case where the opening diameters of the plurality ofdimples are set within a range from 30 to 100 μm and more dimples havingsmaller opening diameters are distributed in comparison to the dimpleshaving larger opening diameters is described in the above embodiment.However, these show one preferable example and the present invention isnot limited to these. It is important to randomly distribute and mix theplurality of dimples having different opening diameters. A ratio of thedistribution may be set to the most relevant value in accordance withthe bearing characteristic number G (fluid viscosity×speed/load) of thesealing face.

For example, the case where 100 nm is adopted as the depth of theplurality of dimples is described in the above embodiment. However, thepresent invention is not limited to this. The depth may be selected froma range from 50 to 1,000 nm. In order to make the sliding characteristicat extremely low speed become preferable, the depth is desirably setwithin a range from 100 to 200 nm.

For example, the case where 40% is adopted as the area ratio of theplurality of dimples relative to the sealing face from a viewpoint toobtain both the sealing and the lubricity at the same time is describedin the above embodiment. However, the present invention is not limitedto this but the area ratio may be set within a range from 30 to 50%.

REFERENCE SIGNS LIST

-   -   1 Sliding part    -   2 Dimple    -   3 Dimple formation region    -   4 Seal face    -   10 Testing machine    -   11 Stationary ring    -   12 Spring    -   13 Casing    -   14 Rotating shaft    -   15 Rotating ring    -   16 Bearing part    -   17 Torque meter    -   18 Load cell    -   S Sealing face

The invention claimed is:
 1. A pair of sliding parts respectively havingsealing faces that slide relative to each other for sealing a sealedfluid that exists in inner or outer peripheries of the sealing faces,each of the sealing faces being a flat surface, wherein: a plurality ofdimples is arranged in a dimple formation region defined on at least oneof sealing faces, the dimple formation region communicating with a highpressure fluid side and being isolated from a low pressure fluid side byonly a flat surface portion of the sealing face, and, wherein: at leastsome of the dimples have different opening diameters, each of theplurality of dimples being isolated from the other dimples by thesealing face in such a manner that the flat surface exists betweenadjoining dimples, the dimples being arranged in such a manner that theplurality of dimples having different opening diameters is randomlydistributed.
 2. The sliding parts as set forth in claim 1, wherein: theopening diameters of the plurality of dimples are set within a rangefrom 30 to 100 μm.
 3. The sliding parts as set forth in claim 1,wherein: depth of the plurality of dimples is set within a range from 50to 1,000 nm.
 4. The sliding parts as set forth in claim 1, wherein: thedepth of the plurality of dimples is set within a range from 100 to 200nm.
 5. The sliding parts as set forth in claim 1, wherein: an area ratioof the plurality of dimples relative to the sealing face is 30 to 50%.6. The sliding parts as set forth in claim 1, wherein: a plurality ofthe dimple formation regions are defined on the sealing face, and thedimple formation regions are arranged so that the flat surface existsbetween adjoining two of the dimple formation regions.
 7. The slidingparts as set forth in claim 2, wherein: the dimple formation regions arealigned in a circumferential direction.
 8. The sliding parts as setforth in claim 1, wherein: some of the dimples adjacent to the highpressure fluid side are opened at a circumferential surface of thesliding part to directly communicate with the high pressure fluid side.9. The sliding parts as set forth in claim 1, wherein: more of thedimples having smaller opening diameters are distributed in comparisonto the dimples having larger opening diameters.